Add missing <exception> include.

[kalaxy]

Clang with libc++ and -std=c++23 fails to compile with:

error: no member named 'terminate' in namespace 'std'; did you mean 'template'?

This change ensures the definition of std::terminate() is available for this scenario by adding the relevant include.

Steps to reproduce on a mac:

1. Create a file to compile: cat test.cpp

#include <boost/safe_numerics/safe_integer.hpp>

2. Compile the file with clang, libc++ and c++23 standard. Note this uses a copy of boost 1.90 installed by conan.

$ clang test.cpp -c -o test.o -I/Users/kalaxy/.conan2/p/b/boostb7f879e062319/p/include -std=c++23

3. Observe the error messages

/Users/kalaxy/.conan2/p/b/boostb7f879e062319/p/include/boost/safe_numerics/checked_result_operations.hpp:40:14: error: no member named 'terminate' in namespace 'std'; did you mean 'template'?
   40 |         std::terminate();
      |         ~~~~~^~~~~~~~~
      |              template
/Users/kalaxy/.conan2/p/b/boostb7f879e062319/p/include/boost/safe_numerics/checked_result_operations.hpp:40:23: error: expected unqualified-id
   40 |         std::terminate();
      |                       ^
...

Side note: It may be worth noting that this did work for earlier versions of the c++ standard. For instance, -std=c++20 works fine. So this might have to do with some of the constexpr changes in c++23 which can cause earlier evaluation of templates.

This fix addresses issue #139.